I read this reply at one of the PhD forums and thought I should share it here. Business PhDs abroad are paid a lot (same is the case with ISB). This was a reply to why they are paid a lot compared to PhDs from other fields (engineering, science):
"A better question might be to ask "why are Ph.D.s so over-produced in other disciplines?" The answer is funding:In the physical sciences, humanities, and most other social-sciences the number of professors in a department is determined as a function of the number of students in a department. With a smaller number of masters students needed to justify a professor and an even smaller number of doctoral students needed to justify a professor.
So the incentive is toward ever larger grad programs.
Now why doesn't this hold in the school of business? The answer is funding:
MBAs are professionals, they are getting a degree that helps them professionally and which is often payed for by their employer. These are not people that would have done a masters in communications or psychology were the business school to close; they are attending in order to obtain a professional degree. As such MBAs fund schools of business in the same way grants and doctoral students fund other schools. But that's where the similarity ends.
MBAs are in no way trained to do research. The MBA is a practitioner's degree, it is enough to move you up the corporate latter, enough to get a job as a consultant, even enough to get you a lecturer/community college professor position if your interest is teaching. Further, Ph.D. programs cost money instead of making it for the department. 
On top of this, the AACSB grants legitimacy to schools of business. Without AACSB accreditation an MBA program often cannot get firms to pay for its students to attend MBA programs. Further, it is nearly clich ล  when someone says "while AACSB accreditation doesn't mean your program is good, not having it does mean that your program is bad". The thing about getting AACSB accreditation is that you have to have a significant portion of your faculty come from AACSB accredited universities.
The AACSB has accredited a total of 127 schools in the US to provide doctoral degrees. Of those most fields have 80 or fewer programs that focus on their particular discipline. Each program graduates, on average, shy of three people a year. Further, there more than 400 AACSB accredited MBA programs which need AACSB accredited Ph.D.s to maintain their accreditation and another 300 'member' programs that do not yet have accreditation, but must have doctoral students from accredited programs in order to obtain it. 
This means that there are 80 universities producing 240 people a year, per field, to feed 700 universities that need AACSB accredited people. This leaves the other 2,000 universities scrambling to find anyone to teach any level of business.
In comparison there are over 1200 people a year that graduate in non-clinical psychology every year.So with five times less competition in the business school, you can see why pay is high and tenure-track jobs are plentiful."